Would you be able to use the same method using just your rope, not a cordelette, and not 'closing the system' like in the video. Leaving one end tied just to you and the other to the climber? Or would you need to close the system.

Would you be able to use the same method using just your rope, not a cordelette, and not 'closing the system' like in the video. Leaving one end tied just to you and the other to the climber? Or would you need to close the system.

Yes, but (and there always is one) doing so will use a lot of rope and your masterpoint knot will be epic in size.